In an individual wheel suspension of this type, a disadvantageous toe-in behavior can occur merely as the result of the lengthwise elastic arrangement of the trailing arm-lengthwise arm on the vehicle body due to longitudinal and/or circumferential forces as well as lateral forces on the wheel.
An object of the invention is to improve an individual wheel suspension of the aforementioned type such that elastic lengthwise springing, desired for comfort reasons, is achieved without undesired toe-in behavior.
This and other objects of the invention are achieved by providing in an individual wheel suspension of the aforementioned type that the articulation of the lengthwise arm is disposed in the vicinity of the wheel center plane with the articulations of the wishbones on the body side being on one side of the wheel axle as viewed from above, and in that the articulations of the wishbones on the wheel side as viewed from above lie approximately on an auxiliary tie rod which runs centrally through the articulations of the wishbone on the body side and at least approximately through the intersection of the application lines of the forces along the wheel and laterally with respect to the wheel. The articulation of the lengthwise arm to the vehicle body is an elastic bearing with different spring rates C.sub.1 and C.sub.2 in directions which are approximately horizontal and approximately perpendicular with respect to one another, and wherein the direction of the first spring rate C.sub.1 is primarily at right angles to the length of the vehicle and forms an angle which is not 90.degree. with the force which results and acts upon the elastic bearing as viewed from above.
The invention produces an individual wheel suspension with the advantage of achieving desired toe-in behavior through elastic lengthwise springing produced by lengthwise and/or lateral forces.
The arrangement of the articulations of the wishbones and lengthwise-arm articulations according to the invention, as well as their design as elastic bearings with spring rates directed in different directions, on the one hand, and the adjustment of the force resulting from the lengthwise and/or lateral force on the arm articulation to the spring rate C.sub.1, acting primarily in the direction transverse to the vehicle, on the other hand, can be established with the angles and spring-travel ratio as set forth hereinafter for the lengthwise-elastically sprung wheel of the individual wheel suspension, whether the wheel goes into toe-in with lengthwise springing as a result of the longitudinal force (braking, accelerating) and/or lateral force (going around a curve), or the predetermined toe-in is retained, or the toe-in is reduced.
In particular, the ratio for the spring rates C.sub.1 and C.sub.2 are determined as a function of an adjustment angle .alpha. between the direction of said first spring rate C.sub.1 and a reference line in the direction lengthwise with respect to the vehicle, a directional angle .beta. between the reference lines and the resultant force where .alpha.+.beta. is less than 90.degree., and a migration angle .gamma. between the reference line and one direction of migration of the lengthwise arm in the elastic bearing according to: EQU C.sub.2 /C.sub.1 tan (.alpha.+.beta.)/tan (.alpha.-.gamma.).
In a disclosed embodiment of the invention, the lengthwise arm is directed forward in the direction of the length of the vehicle, and the wishbones with their auxiliary tie rods, as viewed from above intersect at least approximately at the intersection of the force acting lengthwise to the wheel and the lateral force, and form an angle .delta. with the wheel axis which has a value which is determined in accordance with the migration angle .gamma. of the lengthwise arm with .gamma. being less than or equal to .delta.. With this arrangement and a tuning of the spring rates C.sub.1,C.sub.2 as a function of the different angles, the articulation point of the lengthwise arm undergoes a displacement at right angles to the direction of the auxiliary tie rods of the wishbones both under load caused by longitudinal forces and/or lateral forces as a consequence of the resulting force on the bearing. In this way, the total trailing arm advantageously undergoes a translation without a change in toe-in of the wheel and without an undesired steering movement.
According to a further feature of the invention, the wishbones with their auxiliary tie rods, as viewed from above, form an angle .delta. with the axis of the wheel which is smaller than the migration angle .gamma.. As a result of this feature, a desired toe-in behavior is achieved in the toe-in direction during braking with both wheels of an axle and when rounding a curve in the wheel on the outside of the curve, and in the toe-out direction during drive by both wheels of an axle and when rounding a curve in the wheel on the inside of the curve.
In a second embodiment of the invention, wherein the lengthwise arm points forward in the direction of the length of the vehicle, the auxiliary tie rod centered with respect to the two wishbones, as viewed from above, intersects with the force acting lengthwise with respect to the wheel in the wheel center plane, in the direction of travel, behind the application line of the lateral force, whereby the migration angle .gamma. of the lengthwise arm with respect to the reference line under the influence of the force acting lengthwise upon the wheel, depending on the magnitude, can be selected to be larger than or equal to the angle .delta. between the wheel axle and/or a plane transverse to the vehicle and the auxiliary tie rod.
With such an individual wheel suspension, two resultant force directions, acting in different directions on the bearing of the lengthwise arm, result from the forces along the wheel and the lateral forces. This produces the advantage of a differentiated toe-in behavior in response to forces directed along the wheel and laterally of the wheels. In particular, if the ratio of spring rates C.sub.1 and C.sub.2 is chosen so that no change in toe-in occurs under lateral forces (the articulation point of the lengthwise arm moves at right angles to the direction of the auxiliary tie rods of the wishbones) a change in toe-in in the toe-in direction is feasible under the influence of lateral forces on the wheel. In this manner, for example, as regards favorable toe-in behavior, disadvantageous deformations of the elastic bearings in the articulations of the wishbones can be advantageously eliminated.
The mounting of the lengthwise arm according to the invention can be accomplished in simple fashion by using a rubber-elastic turn and slide spring.
An additional feature of the invention involves an individual wheel suspension with the lengthwise arm pointing forward in the direction running lengthwise of the vehicle. The lower wishbone, in a transverse plane running vertically through the wheel center, forms an auxiliary tie rod with a length that is approximately equal to or larger than half the value of an interval which is established from a transverse pole in the vicinity of the wheel center and the upper wishbone. The thus formed auxiliary tie rod, has length which is less than or equal to the lower auxiliary tie rod, whereby the articulation of the lengthwise arm on the vehicle body is chosen to be near the wheel center plane. In this manner an individual wheel suspension is achieved wherein the advantage of a favorable toe-in behavior with elastic lengthwise springing is combined with the advantage of a favorable toe-in behavior at the desired small change in camber as the spring extends and is compressed.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, two embodiments in accordance with the present invention.